Human milk is well-known to contain more than 100 different oligosaccharides, some of which are genetically determined. Unfortunately, the structural similarities of many of these carbohydrates have made it difficult to isolate, identify, and quantify many of these oligosaccharides. Most of the published works on these oligosaccharides have studied these compounds as classes rather than as individual oligosaccharides.
Previous work has shown that certain oligosaccharides may be beneficial biologically. For example, oligosaccharides containing N-acetylglucosamine (GlcNAc) have been demonstrated to stimulate the growth of Lactobacillus bifidus var pennsylvanicus, which protects infants from gastrointestinal infections (Coppa, G., et al., Pediatrics 91:3 (1993) 637-641, this reference as well as all patents and publications cited herein are incorporated by reference). Other reports indicate that human milk oligosaccharides promote growth of the beneficial bacteria Bifidobacterium bifidum, which is assumed to be involved in the healthy development of infants (Thurl, S., et al., Journal of Chromatography 568 (1991) 291-300). In one study, human milk prevented the attachment of Streptococcus pneumoniae and Haemophilus influenzae (Andersson, B., et al., J. Infect. Dis. 153 (1986) 232-237). This study further proved that this decrease in attachment was "due mainly to components other than the specific antibodies" present in the milk and may be caused by the "receptor-active oligosaccharide determinants on glycoproteins". Pneumococcal attachment was inhibited by both high and low molecular weight fractions, specifically lactose-N-tetraose (LNT, Gal.beta.1-4GlcNAc.beta.1-4Gal.beta.1-4Glc) and lactose-N-neotetraose (LNnT, Gal.beta.1-4GlcNAc.beta.1-3Gal.beta.1-4Glc) (Anderson, B., et al., J. Infect. Dis. 153 (1986) 232-237). In general, oligosaccharides can inhibit the binding of bacteria to epithelial cells, acting as decoys by competing with cell receptors. Additionally, oligosaccharides protect infants from viral and bacterial infections of the respiratory, gastrointestinal, and urogenital tracts.
Genetics play a large part in the presence or absence of certain oligosaccharides in milk from different donors, an attribute which is linked to the Lewis blood group status of the individual. The "Secretor" and "Lewis" genes encode specific glycosyltransferases. These enzymes in turn produce a variety of secondary gene products, specifically, oligosaccharides and other glycoconjugates. The presence or absence of glycosyltransferases in the lactating mammary gland has a direct impact on the existence and quantity of certain carbohydrate structures found in human milk from a given donor.
Many beneficial functions have been attributed to human milk oligosaccharides. For this reason, the supplementation of infant formulas and other pediatric nutritional products with human milk oligosaccharides is desirable. An infant formulation supplemented with oligosaccharides near the naturally occurring levels of such oligosaccharides in human breast milk would be most beneficial. The natural levels of specific human milk oligosaccharides have been obtained from pooled milk samples (Kobata, A., Methods in Enzymology 28 (1972) 262-271; Kunz, C., et al., Acta Paediatr. 82 (1993) 903-912) or by using methods that required heating the samples, thus destroying labile oligosaccharides (Thurl, S. et al., Analytical Biochemistry 235 (1996) 202-206). Also, averages have been published for some oligosaccharide concentrations (See Thurl, S., et al, Ana. Biochem. 235 (1996) 202-206; Thurl, S., et al., J. Chromat. 565 (1991) 291-300), but the variability of these oligosaccharides has not been established because of the large amount of human milk samples necessary to achieve statistical significance. Because of these difficulties, at the present time, an infant formulation containing oligosaccharides near the naturally occurring levels found in human breast milk is not available.